Scientists recognized long ago the possibility of converting heat energy stored in oceans and other large bodies of water into a more useful form of energy such as electricity. The well-known Ocean Thermal Energy Conversion (OTEC) process utilizes the characteristic difference in temperature (20° C.) between solar-warmed surface water and deep cold water to power a closed-cycle or open-cycle heat engine. The closed-cycle approach utilizes a liquid refrigerant or working fluid (ammonia, for example) having a low boiling point. The warm surface water is pumped through an evaporator to boil the refrigerant and produce vapor for driving a low-pressure turbine-generator; and the cold deep water is pumped through a condenser to condense the spent vapor back into a liquid. In the open-cycle approach, the ocean water itself is the working fluid, and the process of boiling (by flash-evaporation typically) and condensing produces fresh (i.e., desalinated) water as a by-product. There are also hybrid systems that boil warm surface ocean water by flash-evaporation and direct the steam through an evaporator to vaporize a closed-cycle working fluid such as ammonia.
In practice, the above-described OTEC processes have met with only limited success because of the relatively small naturally occurring temperature difference between warm surface water and cold deep water. Accordingly, what is needed is an improved way of harnessing solar energy from a body of ocean or fresh water.